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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. interface Interface {
  8. }
  9.  
  10. class Foo implements Interface {
  11. 	Foo(int magicInt) { magicInt = magicInt + 1; /* do some fancy calculations */ }
  12. }
  13.  
  14. class Bar implements Interface {
  15. 	Bar(int magicInt) { magicInt = magicInt + 2; /* do some fancy calculations */ }
  16. }
  17.  
  18. class Factory<T extends Interface> {
  19.     int magicInt = 0; 
  20.  
  21.     T createNewObject(Class<T> typeToMake) {
  22.     	final java.lang.reflect.Constructor<T> magicIntConstructor;
  23.     	try {
  24.     		magicIntConstructor = typeToMake.getDeclaredConstructor(Integer.TYPE);
  25.     	} catch (NoSuchMethodException e) {
  26.     		throw new RuntimeException("No valid constructor!");
  27.     	}
  28.     	final T t;
  29.     	try {
  30.     		t = magicIntConstructor.newInstance(magicInt);
  31.     	} catch (InstantiationException|IllegalAccessException|java.lang.reflect.InvocationTargetException e) {
  32.     		throw new RuntimeException("Couldn't instantiate.");
  33.     	}
  34.     	return t;
  35.     }
  36. }
  37.  
  38. /* Name of the class has to be "Main" only if the class is public. */
  39. class Ideone
  40. {
  41. 	public static void main (String[] args) throws java.lang.Exception
  42. 	{
  43. 		Factory<Foo> fooFactory = new Factory<Foo>();
  44. 		Foo foo = fooFactory.createNewObject(Foo.class);
  45. 		System.out.println(foo);
  46.  
  47. 		Factory<Bar> barFactory = new Factory<Bar>();
  48. 		Bar bar = barFactory.createNewObject(Bar.class);
  49. 		System.out.println(bar);
  50. 	}
  51. }
  52.  
Success #stdin #stdout 0.1s 320576KB
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Standard input is empty
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Foo@10dea4e
Bar@1909752
https://ideone.com/Gemm13
For StackOverfow question http://stackoverflow.com/questions/33475730/constructor-to-interface-abstract-class-using-java-generics
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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